In 2009, Sharrouf was jailed for his role in a planned terror attack in Australia led by Mohamed Ali Elomar, the uncle of the man believed to have offered the bounty.

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The senior Mohamed is currently serving a minimum 21-year sentence for the plot, which involved the manufacture of explosives for a "potentially catastrophic" attack.

Gruesome images

Australian Federal Police issued arrest warrants for the younger Elomar and Sharrouf in late July after they posted gruesome images to Twitter of themselves posing with the severed heads of Syrian fighters. It's believed the photos were taken in the Syrian city of Raqqa.

The latest tweets attributed to Elomar came from the now suspended Twitter handle @abu hafs ozzie.

"Any details were he works or knows if his got kids which school they attend. Like I said I am willing to pay $1000 just for details," another tweet said.

"It was shocking to be honest," Rifi told CNN. "I've taken it extremely seriously because they labeled me as a habashi dog -- even though I've never been a habashi and I'm not a habashi. What it means in their twisted mentally (is that) attacking me, killing me is permissible for followers of their ideology."

Security stepped up

Police are also taking the threat seriously. Rifi said the New South Wales Police Commissioner phoned him before sending officers to his house for a security audit.

Patrols have been stepped up in the area and his son's school principal has suggested he stay at home.

However, Rifi said he refused to be silenced.

"I'm not going into hiding. I know I'm fortunate enough to life in a country where law and order prevail and people can't take matters into their own hands, and affords me the freedom to speak. And I want to use that privilege to defend what we have in Australia and to keep it."

to know my address just ask your dad,we were in same soccer team then and we still Best mates and he knows I am and never been a HABASHI

In a direct message to Elomar, Rifi tweeted: "to know my address just ask your dad, we were in the same soccer team then and we still Best mates and he knows I am and never been a HABASHI."

Old family friends

Rifi is a longtime friend of Elomar's father, Mamdouh Elomar. They met as children in Lebanon before moving to Australia.

Elomar fled the civil war in the 1970s and built a successful engineering business in Sydney. Rifi followed in the early 1980s and has become a respected member of the community for his efforts in breaking down religious barriers.

The Elomars are a "great" family, Rifi said, adding that Mohamed was the "black sheep" who turned his back on what was a stable and supportive upbringing to follow a "twisted ideology."

Mohamed's father would support him "100%," Rifi said, though he added he hadn't spoken to him since the threats were made.

On Thursday, he and Australia's Grand Mufti, Ibrahim Abu Mohamed, gave a series of interviews in Arabic and English to try to counter the recruitment campaign being waged by ISIS militants on social media.

"We're telling young people: 'Forget the rhetoric, look at the action.' And the action they are doing is totally unIslamic," Rifi said.

"While they're pretending to defend Islam, in reality what they're doing is hurting their family, their community and they're giving a distorted image of their religion."

these keyboard warriors do not scare me at all.الساكت عن الحق شيطان اخرس

Extra revulsion was reserved this week for Sharrouf, who posted a picture of his young son holding a man's severed head.

"It is really one of the most disturbing, stomach-turning, grotesque photographs ever displayed," said U.S. Secretary of State John Kerry.

The image was used by U.S. and Australian officials to emphasize the importance of the fight against ISIS militants, who are engaged in a brutal campaign in Iraq and Syria with the aim of establishing an Islamic caliphate.

Around 150 Australians are thought to be supporting their activities, while around 60 are believed to be engaged in active fighting.

"There are a significant number of Australian citizens who are taking part in activities in Iraq and parts of Syria: extremist activities, terrorist activities," Australian Foreign Minister Julie Bishop said.

"Our fear is that they will return home to Australia as hardened homegrown terrorists and seek to continue their work here in Australia."